Blood samples are routinely taken in clinics, hospitals or specialized labs by trained professional for diagnostic purposes. A more cost effective and less invasive alternative to traditional venipuncture method is collecting blood by finger stick on a filter paper. The blood is then dried and sample known as dried blood spot (DBS) can be stored or processed as required. The DBS can then be used for analysis of various small molecules, metabolites, proteins etc. DBS is a powerful blood sampling procedure as it allows collection of blood at any time or place. No special training is required to collect the blood and the blood can be stored or shipped at ambient temperature for a period of time.
One major drawback associated with DBS is the difficulty in quantitating the analytes as the volume of blood loaded cannot be ascertained when directly loaded onto the filter paper in non-lab settings. Volumetric application of blood is not practical when collecting samples in the field. A number of factors influence the spread of blood on a substrate like filter paper. The hematocrit of blood greatly influences the spread of blood on the filter paper (higher hematocrit blood spreads less compared to low hematocrit blood). Also there is differential spread of the blood due to capillary effect (blood spreads more on thinner paper compared to thicker paper). Finally, the chromatographic effect results in uneven distribution of blood components (some blood components may move faster than others). So, one area of the DBS may have different composition than another area. Therefore, the often used practice of punching out specific sizes of blood spots may not be as accurate as processing the whole blood sample entirely collected on the filter.
Different methods have been proposed to overcome the difficulty in quantitating the analytes from DBS. One method proposes quantitating amount of endogenous potassium levels to calculate the hematocrit of loaded blood. While this method reports accurate estimation of hematocrit, it requires additional processing and analysis of blood samples and filter paper. Another method uses diffuse reflection to estimate the hematocrit of blood in the DBS to allow for sample volume correction. While accurate, this method requires additional expensive lab equipment, sample processing and specialized software to analyze the DBS.
Accordingly, there exists an urgent need in the relevant field for a technique that provides accurate estimation of blood volume. Such techniques should be capable of being performed in a cost effective manner, as the whole purpose of DBS technology is to reduce the expenses associated with blood collection, storage and shipment. Such techniques should also allow for estimation of the blood volume in the entire spot, so that analytes can be quantitated accurately.
Furthermore, current devices known in the art used to scan blood samples, including dried blood spots on filter paper, suffer from problems such as high risk of contamination of samples, difficulty in keeping multiple samples organized, isolating samples from human exposure, and limited ability to quickly, efficiently and consistently process multiple samples or batches of samples. Accordingly, there also exists a need in the relevant field for devices that overcome these limitations of the prior art, including devices that may be used in conjunction with the novel techniques disclosed herein.